1. Field of the Invention
The present invention relates to a sheet for sublimation transfer to be used in a thermal transfer recording apparatus, such as a thermal printer, a thermal typewriter, a laser printer and so forth.
2. Description of the Prior Art
In such kind of a sheet for sublimation transfer, a lubricative heat resisting layer is provided on the backside of a material sheet. An ink layer is formed on the surface of the sheet by coating an ink containing dispersing dyes or the like which sublimate by heating. From the backside of the sheet where the lubricative heat resisting layer is formed, thermal transfer corresponding to an image information is performed by means of a thermal head, laser or so forth to transfer the image on to an object, to which the image is to be transferred.
Conventionally, the ink contains a binder in addition to sublimation type dyes. As such binder, in addition to a saturated polyester resin, polycarbonate resin, cellulosic resin, polyvinyl acetoacetal resin (Japanese Patent Laid Open (Kokai) No. 63-151484) and polyvinyl butyral resin (Japanese Patent Laid Open (Kokai) No. 60-101087) among polyvinyl acetal resins are used.
Namely, in the following formula (I) expressing a vinyl acetal group (X), polyvinyl acetoacetal resin contains CH.sub.3 as alkyl group R and polyvinyl butyral resin contains C.sub.3 H.sub.7. ##STR2##
Among the conventional binders saturated polyester resin or polycarbonate resin have relatively high capability of dispersing dyes. However, these resins are defective in a tendency of melting on a printing paper during thermal transfer. On the other hand, polyvinyl acetoacetal resin, polyvinyl butyral resin, or the cellulosic resin, such as ethyl cellulose, propyl cellulose and the like have a property of hardly melting on the printing paper. However, these binder materials have a defect in insufficient holding capability of the dispersing dyes. For instance, the above-mentioned binders are added to respective inks of yellow, magenta, and cyan. Then, respective ink is coated on a material sheet in order of yellow, magenta and cyan to prepare a sheet for sublimation transfer. Then such sheet is wound on a tube of vinyl chloride having a diameter of 1 inch for a plurality of turns, and maintained within a thermostatic chamber at 60.degree. C. for 96 hours. Then, there is observed a dye transferring phenomenon to transfer the dispersing dyes forming yellow, magenta and cyan in the ink layer to the lubricative heat resisting layer on the backside of the material sheet.